1. Field of the Invention
The present invention relates to improved multipoint ranging devices which have a plurality of ranging areas in an observing frame or a shooting frame, and which calculate ranging information by a so-called phase difference method.
2. Description of the Related Art
In ranging devices using the phase difference method, two images of an object are formed by a pair of receiver lenses and detected by image sensors: the ranging device may be either a TTL type or a Non-TTL type.
The distance between the two images formed on the image sensors is determined by repeating a correlation calculation, and the amount of defocus or the distance to an object is calculated. Since a high load is placed on a CPU due to the correlation calculation, the amount of calculation must be reduced in order to reduce the calculation time.
On the other hand, in the case in which only one ranging area is set at the center of the shooting area, defocusing occurs when a main object is not at the center and a picture in which the main object is in focus cannot be taken.
Accordingly, various systems have been suggested and provided in which ranging operation is performed for a plurality of ranging areas set inside a shooting area. In such systems, pictures in which the main object is in focus can be taken even when the main object is not at the center of the shooting area.
However, the amount of calculation in the phase difference method is naturally large, and a high load is placed on the CPU even when the range data for only one ranging area is calculated. Accordingly, the release time-lag is long compared with other methods. Therefore, when the range data is calculated for a plurality of ranging areas, the release time-lag is further increased.
Accordingly, in Japanese Unexamined Patent Application Publication No. 7-110435, a technique is disclosed in which a contrast is determined for each ranging area and the main object is assumed to be at the ranging area corresponding to the maximum contrast. The distance calculation by the phase difference method is performed only for the ranging area in which the main object is assumed to be, so that the release time-lag is minimized.
In contrast, in Japanese Unexamined Patent Application Publication No. 2000-89098, a technique is disclosed in which a correlation calculation by the phase difference method is performed and the object distance is determined for each of the ranging areas. However, since the object is likely to be at the center of the shooting area under normal conditions, a shift range of the correlation calculation is set to be smaller for the ranging areas away from the center of the shooting area (peripheral areas) compared with the ranging area at the center of the shooting area. More specifically, in ranging areas away from the center of the shooting area, the distance range in which the object distance can be determined is limited only to distant regions so as to reduce the number of correlation calculations and the calculation time.
Accordingly, an object of the present invention is to provide a multipoint ranging device in which a correlation calculation is performed for each of a plurality of ranging areas without limiting the distance range in which the object distance can be determined in certain ranging areas, while still reducing the time for obtaining the result of a ranging operation.
According to one aspect, the present invention relates to a distance/defocus detection device which includes a sensor unit formed of a first sensor and a second sensor, the sensor unit receiving an object image in each of a plurality of areas set in a frame, and a calculator which calculates the distance to the object or an amount of defocus in each of the plurality of areas on the basis of a correlation between the image received by the first sensor and the image received by the second sensor, the correlation being determined while shifting the image signal of the first sensor relative to the image signal of the second sensor. The distance/defocus detection device includes a shift-range determination circuit which, after the correlation calculation is performed for a predetermined area, determines a shift range of the correlation calculation for a subsequent area of the plurality of areas on the basis of the result of the correlation calculation for the predetermined area.
According to another aspect, the present invention relates to a distance/defocus detection device which includes a sensor unit formed of a first sensor and a second sensor, the sensor unit receiving an object image in each of a plurality of areas, and a calculator which calculates the distance to the object or an amount of defocus in each of the plurality of areas on the basis of a correlation between the image received by the first sensor and the image received by the second sensor, the correlation being determined by shifting an image signal of the first sensor relative to an image signal of the second sensor. The distance/defocus detection device includes a setting circuit, which sets a shift-start position of the correlation calculation for each of the plurality of areas, and a shift-range determination circuit, which, after the correlation calculation is performed for a predetermined area, determines a shift-start position of the correlation calculation for a subsequent area, on the basis of the result of the correlation calculation for the predetermined area, and outputs the shift-start position to the setting circuit.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.